1. Field of the Invention
The present invention relates to a magnetic recording medium having a recording layer divided in a number of recording elements by a predetermined concavo-convex pattern, and its manufacturing method.
2. Description of the Related Art
There has been a remarkable increase in areal density of magnetic recording media such as hard discs by various improvements including reduction in the grain size of magnetic particles forming the recording layer, material changes, and increased precision in the processing of magnetic heads. Also, perpendicular recording type magnetic recording media, which have an enhanced areal density because of the recording layer having magnetic anisotropy in a direction perpendicular to surface, with a soft magnetic underlayer for further intensifying the recording magnetic field, are being put in use, and a further improvement in the areal density is expected.
On the other hand, it has become evident that existing techniques for increasing the areal density have reached their limits because of processing limits of magnetic heads, the problem of erroneous writing of data on adjacent tracks caused by spreading magnetic fields of the recording head, and the problem of crosstalk at the time of reproducing. Accordingly, magnetic recording media such as a discrete track medium and a patterned medium, in which a recording layer is formed in a predetermined concavo-convex pattern, are being developed as an alternative medium that enables a further increase in the areal density (see, for example, Japanese Patent Laid-Open Publication No. Hei 7-129953). Dry etching techniques can typically be used for the processing of a recording layer in a concavo-convex pattern.
To achieve good recording/reproducing characteristics, it is preferable that the recording layer be formed only as convex portions which are recording elements, and that the recording elements are completely divided from each other to the face on the substrate side. The concavo-convex pattern should be as flat as possible from the viewpoint of flying stability of head sliders, and so the concave portions should be preferably filled with a non-magnetic material to flatten the medium surface. From a manufacturing point of view, the concave portions of the concavo-convex pattern should have a minimum possible depth for the filling/flattening process. That is, the concave portions of the concavo-convex pattern should preferably be formed precisely to a depth that reaches the face on the substrate side of the recording layer.
However, in the processing of the recording layer into the concavo-convex pattern, precise formation of the concave portions to the depth that reaches the face on the substrate side of the recording layer is hard to achieve; it was usually the case that the soft magnetic layer under the recording layer was also processed in an attempt to thoroughly divide the recording elements from each other to the face on the substrate side. The soft magnetic layer usually has controlled magnetic domains and magnetic anisotropy in a direction perpendicular to the track direction (moving direction of the head), and partial processing of the soft magnetic layer will destroy these magnetic domains and anisotropy and increase magnetic noises, leading to deterioration of recording/reproducing characteristics. Moreover, with the concave portions being formed into the layer under the recording layer, the concave/convex height becomes larger, which may lower the head flying stability and deteriorate recording/reproducing characteristics.
These problems could be solved if the processing could be stopped before reaching to the face on the substrate side of the recording layer, but part of recording layer remaining in the concave portions may cause increased magnetic noises and deterioration of recording/reproducing characteristics.